F_VN_MeasureEdgeDistance

Measure the distance between 2 parallel edges, using an interpolation method.
Can use available TwinCAT Job Tasks for executing parallel code regions.
Can return partial results when canceled by Watchdog.

Syntax

Definition:

FUNCTION F_VN_MeasureEdgeDistance : HRESULT
VAR_INPUT
    ipSrcImage     : ITcVnImage;
END_VAR
VAR_IN_OUT
    fAvgDistance   : REAL;
    aStartPoint    : TcVnPoint2_REAL;
    aEndPoint      : TcVnPoint2_REAL;
END_VAR
VAR_INPUT
    eEdgeDirection : ETcVnEdgeDirection;
    fMinStrength   : REAL;
    nSearchLines   : UDINT;
    hrPrev         : HRESULT;
END_VAR

Inputs

Name	Type	Description
ipSrcImage	ITcVnImage	Source image (1 channel)
eEdgeDirection	ETcVnEdgeDirection	Specification of the edge direction from aStartPoint to aEndPoint to search for
fMinStrength	REAL	Specification of the minimum strength (intensity difference) of the edge to search for
nSearchLines	UDINT	Width of the search window, i.e. the number of search lines (1, 3, 5, 7, ...), centered around the line specified by aStartPoint and aEndPoint
hrPrev	HRESULT	HRESULT indicating the result of previous operations (If SUCCEEDED(hrPrev) equals false, no operation is executed.)

In/Outputs

Name	Type	Description
fAvgDistance	REAL	Returns the average distance between the detected edges
aStartPoint	TcVnPoint2_REAL	Position from which to start the search process (in the direction of aEndPoint)
aEndPoint	TcVnPoint2_REAL	Position where the search process ends

Return value

HRESULT

Further information

The function F_VN_MeasureEdgeDistance localizes two linear edges and measures the average distance between them.

Parameter

Input image

The input image ipSrcImage must be a 1-channel grayscale image.

Minimum distance ^{(Return value)}

The parameter fAvgDistance returns the minimum distance between the two localized edges.

Parameters for edge localization

The remaining parameters are explained in detail in the chapter Edge localization.

Expert parameters

The expert version F_VN_MeasureEdgeDistanceExp contains additional parameters.

Application

The measurement of an edge distance looks like this, for example:

hr := F_VN_MeasureEdgeDistance(
    ipSrcImage             :=   ipImageIn, 
    fAvgDistance           :=   fDistance
    aStartPoint            :=   aStartPoint, 
    aEndPoint              :=   aEndPoint,
    eEdgeDirection         :=   TCVN_ED_LIGHT_TO_DARK,
    fMinStrength           :=   fMinStrength, 
    nSearchLines           :=   nSearchLines, 
    hrPrev                 :=   hr
);

Related functions

ClosestPointsBF for calculating the closest points in two point clouds
MeasureAngleBetweenEdges for measuring the angle between two edges
MeasureEdgeDistance for measuring the average distance between two edges
MeasureMinEdgeDistance for measuring the minimum distance between two edges

Required License

TC3 Vision Metrology 2D

System Requirements

Development environment	Target platform	PLC libraries to include
TwinCAT V3.1.4024.54 or later	PC or CX (x64) with PL50, e.g. Intel 4-core Atom CPU	Tc3_Vision